SOURCE

<div class="line line-left line1"></div>

.line {
  background: #01dde8;  
  height: 4px;  
  position: absolute;
  transform-origin: left top;
  z-index: 10;
  
  width: 200px; 
  top: 50px;  
  left: 50px;  
  transform: rotateZ(35deg);  
}

 
.line-left::before {
  content: "";
  position: absolute;
  height: 4px;  
  width: 40px; 
  background: linear-gradient(to left, transparent, #fff);  
  animation: fade-left 3s linear infinite;  
  box-shadow: 0px 0px 17px 5px #72dffa; 
}

 
@keyframes fade-left {
  0% {
    right: 0px;
    opacity: 0;
  }
  10% {
    opacity: 1;
  }
  90% {
    opacity: 1;
  }
  100% {
    right: calc(100% - 40px);  
    opacity: 0;
  }
}